1. Field of the Invention
The present invention relates to a sheet feeding device of the type including a belt or similar feeding means and a reverse roller or similar separating member driven in a direction opposite to a direction of sheet feed, a sheet conveying device, and an image scanning apparatus and an image forming apparatus including the same.
2. Description of the Background Art
A problem with a sheet feeding device of the type described is that a belt and a reverse roller hit against each other at the time of conveying operation effected between consecutive sheets. This accelerates the wear of the belt and thereby reduces the life of the belt. Another problem is that when, e.g., sheets with information written in pencil are conveyed, the information is transferred from the preceding sheet to the belt and then from the belt to the following sheet, smearing the following sheet.
To promote accurate sheet conveyance while obviating the wear of a feed roller, Japanese Patent Laid-Open Publication Nos. 4-350033, 10-297778 and 7-232831, for example, propose to release feeding means from a sheet when the sheet is conveyed to conveying means positioned downstream of the feeding means.
Japanese Patent Application No. 12-101739, for example, teaches a sheet feeding device including a separating mechanism made up of a belt and a reverse roller. In this sheet feeding device, a spacing member adjoins the belt for spacing the reverse roller and belt. When a single sheet is conveyed from a nip between the belt and the reverse roller to a preselected position downstream of the nip in the direction of sheet feed, the spacing member releases the belt and reverse roller from each other. The above document describes that such a configuration minimizes the contact of the belt and reverse roller and that of the belt and documents without impairing the sheet feeding and separating ability, thereby reducing the wear of the belt and the smearing of the belt.
Japanese Patent Laid-Open Publication No. 11-180570, for example, proposes to insure accurate sheet feed with a stop in a sheet feeding device of the type described above. The stop is configured to prevent the belt from rotating in the direction opposite to the direction of sheet feed by being driven by the reverse roller. Japanese Patent Laid-Open Publication No. 8-310669 discloses a driveline assigned to a belt and including a one-way clutch that allows the belt to rotate only in the direction of sheet feed. Such a driveline does not disturb the order of pages of documents or fail to feed documents.
Japanese Patent Laid-Open Publication No. 11-143139 teaches a sheet feeding device including a single drive means for causing a pickup roller and a stop to move into and out of contact with each other. The rotation of a single pickup motor is delivered via two drivelines, so that the single drive means can drive both of the pickup roller and stop. This successfully reduces the number of parts of the drive means.
Japanese Patent Laid-Open Publication No. 11-217126, for example, discloses a sheet feeding device including a member for varying the pressing position of a belt via a belt bracket. More specifically the above member mechanically varies the contact angle of the belt and therefore a separating pressure derived from the tension of the belt, thereby making the pressure optimal in accordance with the kind of documents.
However, the conventional sheet feeding devices of the type including a feeding mechanism including a belt and a reverse roller do not give sufficient consideration to the following point. When the belt is released from the reverse roller, the reverse roller returns a sheet contacting it in the reverse direction opposite to the direction of sheet feed when driven in the reverse direction. More specifically, the reverse roller returns, among two or more sheets paid out thereto, only one sheet contacting it to the upstream side due to friction acting between the reverse roller and the sheet. As a result, it is likely that the order of pages of the one sheet and sheets overlying it is disturbed or the one sheet is not fed. For example, if the one sheet returned is a sheet being fed, then the pickup roller does not pay out the one sheet, but pays out the next sheet. If the returned sheet is the last sheet, then it is left on a tray without being fed.
Particularly, in the sheet feeding device taught in Application No. 2000-101739 mentioned earlier, circular collars (spacing members) rotatably supported at both sides of the belt are pressed against and then released from the reverse roller during the conveyance of a document. While the collars are in such a movement, a nip angle between the belt and the reverse roller is apt to vary and effect the separating ability. The sheet feeding device disclosed in Laid-Open Publication No. 11-143139 mentioned earlier does not give any consideration to an arrangement for releasing the belt and reverse roller. Further, the sheet feeding device proposed in Laid-Open Publication No. 11-217126 mentioned earlier needs an exclusive mechanism for varying the separation pressure, resulting an increase in cost.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 11-143139 and 11-217126.
It is an object of the present invention to provide a sheet feeding device capable of releasing a belt and a reverse roller to thereby reduce contact between the belt and a sheet without impairing a sheet feeding and separating ability, a sheet feeding device and an image scanning apparatus and an image forming apparatus using the same.
It is another object of the present invention to provide a sheet feeding device capable of dealing with various kinds of sheets with a simple construction, a sheet conveying device and an image scanning apparatus and an image forming apparatus using the same.
In accordance with the present invention, a sheet feeding device includes a feeding section for feeding sheets with a belt, a separating member for separating the sheets one by one in contact with the belt, and a spacing member adjoining the belt for spacing the separating member and belt. The spacing member spaces the belt and separating member when a single sheet is conveyed from a nip between the belt and the separating member to a preselected position downstream of the nip in a direction of sheet feed.
A sheet conveying device including the above sheet feeding device and an image scanning apparatus and an image forming apparatus including them each are also disclosed.